Tomato bacterial endophytes in controlling Verticillium wilt and their advantage on biostimulation

Abstract

Summary A total of 688 bacterial endophytes were isolated from both greenhouse and field-grown tomatoes in the Tehran and Alborz provinces, Iran in order to obtain effective bacterial endophytes against the fungus Verticillium dahliae. 128 bacterial isolates, with respect to their different phenotypic characteristics were further analysed. All bacteria with positive hypersensitivity reaction on tobacco and geranium leaves and potato soft rot were eliminated, and totally 39 isolates were selected for in vitro antagonism and greenhouse tests. The potential biocontrol isolates were evaluated using seed treatment and soil drench methods on two tomato cultivars. The results indicated that seven bacterial isolates had a high potential for the control of the fungus and reduced the severity disease to 95-98%. This reduction was coincided with an increase in some growth factors like plant dry weight, root dry weight, plant height, root length, root fresh weight and plant fresh weight ranged between 92-98%. The seven antagonists’ preliminary identification was confirmed using 16SrRNA gene sequencing analysis. The BLAST analysis was performed, and the bacteria were also identified as Bacillus pumilus (two isolates), Bacillus subtilis, Bacillus safensis, Enterobacter ludwigi, Serratia marcesens and Pseudomonas beatica. Biocontrol mechanisms examination indicated that protease production was positive for all isolates and differentiated isolates E. ludwigii and P. beatica as higher producers with protease levels up to 65%. The three bacteriocins producing isolates inhibited the phytopathogenic mycelium up to 70% in dual culture assay. Also, five of the isolates produced siderophores and P. baetica, S. marcesens and E. ludwigii produced remarkable amount of auxin hormone.